286 Dr. II. Herwig's Investigations on the Conformity 



stances. Unfortunately these experiments are not very numerous 

 (in all about twenty). 



Quite recently Horstman has published* experiments on the 

 interdependence of the pressure, volume, and temperature of the 

 vapours of bisulphide of carbon and of ether; but these he does 

 not consider sufficiently trustworthy to warrant the deduction of 

 a law from them. More correct are his experiments on the inter- 

 dependence of temperature and vapour-densit}^, under a pressure 

 of one atmosphere, for ether, water, and acetic acid, which lead 

 to the same result as the experiments of Cahours. 



The survey of these incomplete observations shows that many 

 experiments are still necessary in order that the problem so 

 peculiarly interesting* for the mechanical theory of heat may 

 meet with its solution. Even for one limit of all the conditions 

 of vapour which come into question here, viz. the case of perfect 

 saturation, a very imperfect support has been afforded by obser- 

 vations to the theoretical speculations concerning the mecha- 

 nical theory of heat. According to a method which I will pre- 

 sently describe, I have attempted to furnish some contributions 

 to the solution of this problem. 



§2. 



The apparatus, which is intended to render a simultaneous 

 variation of pressure, volume, and density possible, was indicated 

 to me by Professor Wullner, to whom I return my best thanks 

 for the friendliness with which he always allows my work to be 

 carried on in his laboratory. 



The vapour was placed over mercury, in a divided carefully 

 calibrated tube [a b, fig. 1, Plate II.), of 3*9 centims. diameter 

 and 48 centims. length, which was firmly clamped, with its lower 

 end open, by means of an india-rubber plug in an iron sheath. 

 By means of a screw and a piece of caoutchouc this sheath was 

 fastened in a cavity in a thick iron plate (r s), 15 centims. long 

 and 10 broad ; in this plate was a second cavity, connected with 

 the former by an interior canal, and in which a smaller iron 

 sheath was similarly fastened. In this last sheath there was 

 fastened, by means of an india-rubber plug, a tube 6'8 centims. 

 wide, 2*6 centims. long, terminating above in a narrow tube (c d), 

 which served as a reservoir for the mercury which would overflow 

 from the calibrated tube when filled with vapour. The apparatus 

 was placed in a copper bath, 64 centims. high, 25 long, and 16 

 broad, in the two front sides of which were glass plates, so that 

 both tubes were visible in their whole circumference during the 

 observation. On the two other sides of the bath there were cases 

 closed at the top and cut out of sheet iron; under these the heating 

 gas-flames could be kept quite steady. The temperature of the bath 

 * Liebig's Avnalen, Suppl. vol. vi. p. i?l. 



